Nerve fiber caliber analysis in the mouse intermediate nerve with electron microscope.

A nerve fiber caliber analysis was performed by electron microscope on 6 intermediate nerves from 5 mice. Majority (86.5%) of the myelin sheaths of the myelinated fibers in the intermediate nerves ranged from 1 to 2 micrometers in minor diameter, and majority (85.7%) of their axons ranged from 0.4 to 1.2 micrometers in minor diameter. The intermediate nerves contained small myelinated fibers at much higher percentage than the large fiber zone of the motor roots of the facial nerves, while it did not show significant difference from the small fiber zone of the motor roots. However, frequency distribution of myelin sheaths of the myelinated fibers of the intermediate nerves may tend to be a little larger than that of the small fiber zone of the motor roots, while frequency distribution of their axons may incline to the more or less smaller than that of the small fiber zone of the motor roots. Majority (72.4%) of the unmyelinated fibers in the intermediate nerves ranged from 0.3 to 0.7 micrometers in minor diameter. Unmyelinated fibers of the intermediate nerves showed similar pattern of diameter frequency distribution with that of the motor roots of the facial nerves and the deep petrosal nerves. The diameter frequency distribution of the myelin sheaths, the axons of the myelinated fibers and the unmyelinated fibers in the intermediate nerves were constantly unimodal.